Where the ring is re-useable, it is typically openable to allow installation over or removal from the flange and rim. Then the ring will usually comprise a circumferential discontinuity which forms a pair of overlappable or opposed ends which are releasably secured together by a releasable fastening or latch mechanism. The groove profile will often be tapered, to draw the flange and rim into engagement with each other as the ring is tightened, and optionally to draw the flange and rim into clamping engagement with an interposed sealing gasket. However such clamping and/or sealing functions need not always be present. Optionally, the ring end fastening or latch mechanism may be provided with an anti-tamper lock pin or similar tamper indicating security seal or tag, to provide some guarantee of the integrity of the container contents. The container and its opening may be of various sizes and shapes, with lids or other closures of a suitable corresponding size and shape. For example the opening and lid may be substantially square, rectangular or other polygonal shape. Typically the lid or closure is round, for fitment to an open-ended cylindrical drum. In the North American market, fibreboard drums with steel end chimes are commonly used together with injection moulded lids. Open-topped blow-moulded plastics drums are also used, again with injection moulded plastics lids. The blow moulded drums predominate in other markets.
Historically the openable securing rings have been made from metal, commonly painted or plated steel. However these are difficult to recycle and are prone to corrosion, or to flaking of the coating. Corrosion or coating particles shed by the ring can contaminate the container contents. There is therefore an increasing use of securing rings made from plastics. U.S. Pat. Nos. 4,194,772, 4,678,216, 5,129,537, 5,713,482, 7,243,962 and US2009/0294449 relate to such plastics securing rings.
To be strong enough to survive normal rough handling of the filled containers, plastics securing rings need to be made with a heavier (thicker) cross-section than a corresponding metal ring. Similarly, the releasable fastening or latch mechanism for the openable ring ends tends to be significantly bulkier in a plastics ring compared to a metal ring. This can lead to a number of problems. One such problem is in container stackability.
During transport and storage it may be desired to stack several layers of containers one on top of another. The lids and bases of the containers described above can be deliberately designed to interfit, so as to improve stacking stability. Or the containers, being of regular shape, can simply be piled up in orderly layers, without interfitting. Bulky securing ring latch or fastening mechanisms can protrude to such an extent that they interfere with the stable and orderly stacking of the containers in layers. The mechanism may project axially of the ring so that it either stands proud of the top surface of the associated container lid, or else projects into the space designed to be occupied by part of an adjacent interfitted container. This part may be, for example, a container base end chime which is designed to fit over and around part of the lid of a container below. The upper container in the stack is thereby prevented from resting squarely on the lower container and will instead lean at an angle and be free to rock, reducing the stack stability and preventing the containers from packing closely together. If one attempts to stack still further layers, leaning of the containers becomes more exaggerated, and each higher layer ever more disorderly, until further stacking may soon be impossible. The weight of the containers above will also impose high transverse loading directly on the ring latch or fastening mechanisms, which have to support up to half of this weight. The ring fastening mechanisms will similarly experience high inertial loads from the containers during transit, in both cases leading to a risk of crushing and failure. The problem is particularly acute in the case of the relatively bulky plastics mechanisms, but can still arise with metal ring latches/fastenings. A crushed metal ring fastening mechanism could jam and make the ring difficult to remove. A crushed plastics ring fastening mechanism is liable to fail completely, potentially releasing the lid and allowing the container contents to spill.